High Tech Pet Yard Barrier Outdoor Pet Barrier Extra Receiver Additional receiver expands the YB-1 Yard Barrier outdoor sonic fence from High Tech Pet Uses sound, not shock, to keep pets out of flower beds and gardens, off porches, away from pools, ponds, trash cans or any other off-limits area Heavy duty waterproof outdoor receiver unit may be placed anywhere that's off-limits to pets Requires transmitter collar model MS-4 (included with Sound Barrier Indoor Sonic Dog & Cat Fence SB-1), MS-2, MS-2A or RX-10 Requires one 9-volt alkaline battery (not included)